|Publication number||US7714548 B1|
|Application number||US 11/937,340|
|Publication date||May 11, 2010|
|Filing date||Nov 8, 2007|
|Priority date||Nov 8, 2007|
|Publication number||11937340, 937340, US 7714548 B1, US 7714548B1, US-B1-7714548, US7714548 B1, US7714548B1|
|Inventors||Ernest Henry Wittenbreder, Jr.|
|Original Assignee||Wittenbreder Jr Ernest Henry|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (17), Referenced by (4), Classifications (10), Legal Events (3)|
|External Links: USPTO, USPTO Assignment, Espacenet|
1. Field of the Invention
The subject invention generally pertains to electronic power conversion circuits, and, more specifically, to high frequency, switched mode electronic power converters. The subject matter relates to new adaptive timing circuits that achieve optimal switch turn on timing for switches in high efficiency zero voltage switching power converters.
2. Description of Related Art
Zero voltage switching (ZVS) power converters have been demonstrated to provide significant efficiency advantages over conventional hard switching power converters, particularly for off line power supplies. The ZVS power converters eliminate drain circuit switching losses and some of the gate circuit switching losses, they eliminate rectifier reverse recovery effects, and, when the die sizes of the switches are optimized for minimum power loss they also achieve significant reductions in channel conduction losses.
In order to achieve the maximum benefit of zero voltage switching it is important to optimally time the zero voltage turn on transition. The problem is illustrated in
For the case in which there is insufficient energy to drive the drain source voltage to zero the adaptive timing circuit illustrated in
An object of the subject invention is to reveal new adaptive gate drive timing circuits that can provide optimal turn on timing for the initial condition in which there is sufficient energy to drive the transition to zero volts and for the initial condition in which there is insufficient energy to drive the turn on transition to zero volts that do not rely on a high voltage rectifier.
Another object of the subject invention is to reveal new adaptive gate drive timing circuits that can provide optimal turn on timing for the initial condition in which there is sufficient energy to drive the transition to zero volts and for the initial condition in which there is insufficient energy to drive the turn on transition to zero volts that can be accomplished with a low voltage ASIC without the use of any high voltage components.
Further objects and advantages of my invention will become apparent from a consideration of the drawings and ensuing description.
These and other objects of the invention are provided by novel circuit techniques that rely on the sensing of a capacitor discharge current and the sensing of the absence of capacitor discharge current to initiate the turn on transition of a main switch in a zero voltage switching power conversion circuit.
The present invention is illustrated by reference to the drawings.
The subject invention reveals new adaptive gate drive timing circuits for achieving optimal switch timing in zero voltage switching power converters for both the energy sufficient initial condition and the energy insufficient initial condition without the use of a high voltage rectifier. The subject invention also reveals a new adaptive gate drive timing circuit that achieves optimal switch timing without the use of any high voltage components.
A discharge current detector circuit with the CDRAIN capacitor is illustrated in
In operation a turn on transition is initiated when a PWM control signal, used for regulating a current or a voltage at an input or output of a power supply, transitions to a logic high state. Prior to the beginning of the turn on transition the PWM control signal is in a logic low state, which forces the Q outputs of flip flop 1 and flip flop 2 to be in logic low states and the Q* outputs of flip flop 1 and flip flop 2 to be in logic high states. A low PWM control signal also forces the output of the NAND gate to be in a logic high state. The output of the discharge current detector circuit is high when there is no discharge current, which is the typical case at the instant that the PWM control signal transitions to the high state initiating the turn on transition. The discharge current detector circuit is biased such that, even if there is a small discharge current, the output of the discharge current detector will be high. Soon after the PWM control signal goes high the drain terminal voltage of MPOWER begins to fall, which forces the output of the discharge current detector circuit to a logic low state. The output of the NAND gate remains high since the output signal of the discharge current detector is in a logic low state. A logic low state at the PR* input of flip flop 1 forces the Q output of flip flop 1 to a logic high state. When the drain voltage of MPOWER has reached a point where it is no longer falling, or falling only very slowly, then the output of the discharge current detector transitions from low to high and the output of the NAND gate transitions from high to low. The logic low output of the NAND gate forces the Q output of flip flop 2 to a high state and causes the driver to enable the gate of MPOWER. Whether the cause of the change in output state of the discharge current detector results from the drain source voltage of MPOWER reaching zero volts or from the drain source voltage of MPOWER reaching a minimum voltage is inconsequential and has the same effect, which is the desired effect of turning on the mosfet MPOWER at the optimal instant. When the gate of MPOWER is enabled the drain of MPOWER begins to fall again, if the drain source voltage has not yet reached zero volts. When the drain source voltage begins to fall again the output of the discharge current detector changes from a logic high state to a logic low state, forcing the output of the NAND gate high. A logic high signal at the PR* input of flip flop 2 has no effect on its outputs, so the turn on transition of MPOWER proceeds without interruption or delay. At the end of the on state of the power supply of which MPOWER is a part the PWM control signal is driven to a logic low state clearing both flip flops so that the Q output of flip flop 2 transitions to a logic low state and the driver drives the gate of MPOWER low initiating a turn off transition. The logic low PWM input to the NAND gate and the logic low input to the NAND gate from flip flop 1 force the NAND gate output to be logic high while the PWM control signal is low so that the Q output of flip flop 2 must remain low as long as the PWM control signal is low, regardless of the output of the discharge current detector circuit.
When the drain voltage is falling rapidly the capacitor CDRAIN is discharging and the non-inverting input to the comparator U1 in
Another embodiment of the subject invention is illustrated in
Another embodiment of the subject invention is illustrated in
Thus the reader will see that an adaptive gate drive timing circuit that relies on detection of a discharge current in a drain connected capacitance can provide optimal switch turn on timing for a zero voltage switching power converter for both energy sufficient and energy insufficient initial conditions, thereby obviating a high voltage rectifier and enabling the use of a low voltage ASIC for optimal switch turn on timing with no high voltage components.
While my above description contains many specificities, these should not be construed as limitations on the scope of the invention, but rather, as exemplifications or preferred embodiments thereof. Many other variations are possible. For example, circuits similar to the circuits shown but with polarity of the input or output reversed or the polarity of switches reversed from that illustrated in the figures shall be considered embodiments of the subject invention. Also, other discharge current detection circuits are possible, including circuits that sense a voltage difference at the terminals of a current sensing resistor placed to conduct all or some of the discharge current and other sequencing circuits are possible using different sets of logic circuit elements. Also the illustrations apply the new technique to a N channel power mosfet, but the technique applies equally to P channel power mosfets, to JFETs, and to IGBTs and bipolar transistors, which should be considered embodiments of the subject invention. Also, my description is illustrated using a PWM control signal, but other forms of modulation are possible to establish the timing necessary for turn on and turn off of the controlled switch and these other modulation forms should be considered embodiments of this invention. Also, the examples provided illustrate the application of the novel adaptive gate drive timing circuit to a ZVS main switch in a power supply, but the adaptive gate drive timing circuit can also be used to drive and optimally time a turn on transition for a synchronous rectifier and that application should be considered an embodiment of the subject invention.
Accordingly, the scope of the invention should be determined not by the embodiments illustrated, but by the appended claims and their legal equivalents.
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|Cooperative Classification||H03K5/153, H03K17/163, H03K17/133, H02M1/083|
|European Classification||H02M1/08C, H03K5/153, H03K17/16B2B, H03K17/13B|
|Dec 20, 2013||REMI||Maintenance fee reminder mailed|
|May 11, 2014||LAPS||Lapse for failure to pay maintenance fees|
|Jul 1, 2014||FP||Expired due to failure to pay maintenance fee|
Effective date: 20140511